Input buffer circuit, semiconductor memory device and memory system

ABSTRACT

An input buffer circuit includes a logic unit, a clock enable buffer, and a clock buffer. The logic unit is configured to receive a clock signal and a clock enable signal, and to output a decision signal indicative of whether the clock signal is normally input, where the decision signal is activated when the clock signal is normally input. The clock enable buffer is configured to buffer the clock enable signal and to activate an internal clock enable signal, in response to an activation of the decision signal. The clock buffer is configured to buffer the clock signal and to output an internal clock signal, in response to an activation of the internal clock enable signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of application Ser. No. 12/851,718,filed Aug. 6, 2010, of which claim of priority under 35 USC §119 is madeto Korean Patent Application No. 2009-0072734, filed on Aug. 7, 2009 inthe Korean Intellectual Property Office (KIPO), the contents of whichare herein incorporated by reference in their entirety.

BACKGROUND

Example embodiments relate to semiconductor devices, more particularly,to input buffer circuits and to semiconductor memory devices and memorysystems including buffer circuits.

In general, semiconductor memory devices receive external clock signals,and operate based on the clock signals as reference timing. For example,synchronous dynamic random access memories (DRAMs) read and write datain synchronization with the external clock signal. Input of the clocksignal and commands to the semiconductor memory device is controlled bya clock enable signal. When the clock enable signal is input to thesemiconductor memory device before the clock signal is input to thesemiconductor memory device (due to various factors such as noise), thesemiconductor memory device may operate according to an incorrectcommand.

SUMMARY

According to some example embodiments, an input buffer circuit of asemiconductor memory device is provided which includes a logic unit, aclock enable buffer, and a clock buffer. The logic unit is configured toreceive a clock signal and a clock enable signal, and to output adecision signal indicative of whether the clock signal is normallyinput, where the decision signal is activated when the clock signal isnormally input. The clock enable buffer is configured to buffer theclock enable signal and to activate an internal clock enable signal, inresponse to an activation of the decision signal. The clock buffer isconfigured to buffer the clock signal and to output an internal clocksignal, in response to an activation of the internal clock enablesignal.

According to some example embodiments, a semiconductor memory device isprovided which includes a memory core unit that includes a memory cellarray, and a buffer unit that includes a plurality of buffers configuredto provide an internal address and internal control signals to thememory core unit in synchronization with an internal clock signal. Thesemiconductor memory device further includes an input buffer circuitwhich includes a clock enable buffer and a clock buffer. The clockenable buffer is configured to activate an internal clock enable signal,in response to a clock signal and a clock enable signal, the internalclock enable signal being activated when the clock signal is normallyinput. The clock buffer is configured to buffer the clock signal toprovide the internal clock signal, in response to an activation of theinternal clock enable signal.

According to some example embodiments, a memory system is provided whichincludes a plurality of memory modules, and a memory controllerconfigured to generate clock enable signals to each of the memorymodules to control an operation of each of the memory modules. Each ofthe memory modules includes

a logic unit, a clock enable buffer and a clock buffer. The logic unitis configured to output a decision signal indicating whether a clocksignal is normally input, in response to the clock signal and the clockenable signal, where the decision signal is activated when the clocksignal is normally input. The clock enable buffer is configured tobuffer the clock enable signal and to activate an internal clock enablesignal, in response to an activation of the decision signal. The clockbuffer is configured to buffer the clock signal to output the internalclock signal, in response to an activation of the internal clock enablesignal.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative, non-limiting example embodiments will be more clearlyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings.

FIG. 1 is a block diagram illustrating an example of an input buffercircuit according to some example embodiments.

FIG. 2A illustrates an example of the logic unit in FIG. 1 according tosome example embodiments.

FIG. 2B illustrates an example of the logic unit in FIG. 1 according tosome example embodiments.

FIG. 3 is a circuit diagram illustrating an example of the clock enablebuffer in FIG. 1 according to some example embodiments.

FIG. 4 is a block diagram illustrating an example of an input buffercircuit according to other example embodiments.

FIG. 5 is a circuit diagram illustrating an example of the voltage leveldetection circuit 400 in FIG. 4 according to some example embodiments.

FIG. 6 is a waveform diagram illustrating an operation of the inputbuffer circuit 20 of FIG. 4.

FIG. 7 is a block diagram illustrating an example of an input buffercircuit according to still other example embodiments.

FIG. 8 is a block diagram illustrating an example of a semiconductormemory device according to example embodiments.

FIG. 9 is a block diagram illustrating an example of the buffer unit inFIG. 8 according to example embodiments.

FIG. 10 is a block diagram illustrating a memory system according tosome example embodiments.

FIG. 11 is a flow chart illustrating a method of controlling asemiconductor memory device according to some example embodiments.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various example embodiments will be described more fully hereinafterwith reference to the accompanying drawings, in which some exampleembodiments are shown. The present inventive concept may, however, beembodied in many different forms and should not be construed as limitedto the example embodiments set forth herein. Rather, these exampleembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the present inventiveconcept to those skilled in the art. In the drawings, the sizes andrelative sizes of layers and regions may be exaggerated for clarity.Like numerals refer to like elements throughout.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are used to distinguish oneelement from another. Thus, a first element discussed below could betermed a second element without departing from the teachings of thepresent inventive concept. As used herein, the term “and/or” includesany and all combinations of one or more of the associated listed items.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between” versus “directly between,” “adjacent” versus “directlyadjacent,” etc.).

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting of thepresent inventive concept. As used herein, the singular forms “a,” “an”and “the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. It will be further understood thatthe terms “comprises” and/or “comprising,” when used in thisspecification, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this inventive concept belongs. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

FIG. 1 is a block diagram illustrating an example of an input buffercircuit according to some example embodiments.

Referring to FIG. 1, an input buffer circuit 10 includes a logic unit100, a clock enable buffer (CKE buffer) 300 and a clock buffer 200.

The logic unit 100 generates a decision signal DS indicating whether ornot a clock signal CK is normally input in response to the clock signalCK and a clock enable signal CKE. That is, the logic unit 100 receivesthe clock signal CK and the clock enable signal CKE, and provides an“activated” decision signal DS when the clock signal CK is normallyinput. For example, the activated decision signal DS can be denoted by agiven logic state, and in this case, a determination as to whether ornot the clock signal CK is normally input is based on a logic level ofthe decision signal DS. As a specific example, when the clock enablesignal CKE is activated before the clock signal CK is normally input,the decision signal DS is first logic level (i.e., logic low level).

The clock enable buffer 300 buffers the clock enable signal CKE toprovide an internal clock enable signal ICKE, in response to anactivation of the decision signal DS. That is, the clock enable buffer300 provides the internal clock enable signal ICKE that is activatedwhen the clock signal CK is normally input.

The clock buffer 200 buffers the clock signal CK to provide the internalclock signal ICK, in response to an activation of the internal clockenable signal ICKE. A semiconductor memory device operates insynchronization with the internal clock signal ICK. Since the clockbuffer 200 buffers the clock signal CK to provide the internal clocksignal ICK when the decision signal DS is activated (when the decisionsignal DS is second logic level (i.e., logic high level)), thesemiconductor memory device may be prevented from operating abnormallywhen the clock signal CK is not input normally.

The clock signal CK may, for example, be a differential signal or asingle-ended signal.

FIG. 2A illustrates an example of the logic unit shown in FIG. 1according to some example embodiments. In particular, FIG. 2Aillustrates an example of the logic unit in FIG. 1 in the case where theclock signal CK is a differential signal.

Referring to FIG. 2A, a logic unit 110 includes an OR gate 112 thatreceives differential clock signals CK1 and CK2, and an AND gate 114that performs an AND operation on an output of the OR gate 112 and theclock enable signal CKE to provide the decision signal DS according to aresult of the AND operation. The OR gate 112 receives the differentialclock signals CK1 and CK2 and performs an OR operation on thedifferential clock signals CK1 and CK2. Accordingly, when thedifferential clock signals CK1 and CK2 are normally input, the output ofthe OR gate 112 is a logic high level. Therefore, the decision signal DSis a logic high level only when the output of the OR gate 112 is a logichigh level, and thus, malfunction may be prevented even when the clockenable signal CKE is activated before the differential clock signals CK1and CK2 are normally input.

FIG. 2B illustrates an example of the logic unit in FIG. 1 according tosome example embodiments. In particular, FIG. 2B illustrates an exampleof the logic unit in FIG. 1 in the case where the clock signal CK is asingle-ended signal.

Referring to FIG. 2B, a logic unit 1200 includes an inverter 122, an ORgate 124 and an AND gate 126. The inverter 122 inverts the clock signalCK. The OR gate performs an OR operation on an output of the inverter122 and the clock signal 124. The AND gate 126 performs an AND operationon an output of the OR gate 124 and the clock enable signal CKE toprovide the decision signal DS according to a result of the ANDoperation. Accordingly, when the clock signal CK is normally input, theoutput of the OR gate 122 is a logic high level. Therefore, the decisionsignal DS is a logic high level only when the output of the OR gate 124is a logic high level. In this manner, malfunction may be prevented whenthe clock enable signal CKE is activated before the clock signal CK isnormally input.

FIG. 3 is a circuit diagram illustrating an example of the clock enablebuffer in FIG. 1 according to some example embodiments.

Referring to FIG. 3, a clock enable buffer 300 includes n-channel metaloxide semiconductor (NMOS) transistors 315 and 316 which respectivelyreceive a reference signal VREF and the clock enable signal CKE, and aNMOS transistor 317 which has a gate receiving an inverted decisionsignal DS from an inverter 321, a drain connected to sources of the NMOStransistors 315 and 316 and a source connected to a ground voltage(GND). The clock enable buffer 300 further includes p-channel metaloxide semiconductor (PMOS) transistors 313, 314, 315 and 316 andinverters 322 and 323. The PMOS transistor 311 has a source connected toa power supply voltage VDD and a diode-connected gate that is connectedto a gate of the PMOS transistor 312. The PMOS transistors 311 and 312form a current mirror. The PMOS transistor 313 has a source connected tothe power supply voltage VDD, a drain connected to a drain of the PMOStransistor 311 and a gate receiving the inverted decision signal DS. ThePMOS transistor 314 has a source connected to the power supply voltageVDD, a gate receiving the inverted decision signal DS and a drainconnected to an input of the inverter 322. The input of the inverter 322is connected to the drains of the PMOS transistors 312 and 314, and theinverter 323 inverts an output of the inverter 322 to provide theinternal clock enable signal ICKE. In the example of FIG. 3, the clockenable signal CKE is buffered to be provided as the internal clockenable signal ICKE only when the decision signal DS is logic high level(that is, the clock signal CK is normally input).

The input buffer circuit 100 of FIG. 1 illustrates a configuration of aninput buffer circuit included in a semiconductor memory device when thesemiconductor memory device is in normal operation mode.

In a power-up mode when a power supply voltage is initially applied tothe semiconductor memory device, the clock enable signal CKE may beactivated thereby to cause malfunction of the semiconductor memorydevice due to external noises before the power supply voltage reaches atarget level.

FIG. 4 is a block diagram illustrating an example of an input buffercircuit according to other example embodiments.

An input buffer circuit 20 of FIG. 4 is an input buffer circuit when thepower-up mode of the semiconductor memory device is considered.

Referring to FIG. 4, the input buffer circuit 20 includes the logic unit100, the clock enable buffer 300 and the clock buffer 200 also includedin the input buffer circuit 10 of FIG. 1. The example of FIG. 4 differsfrom that of FIG. 1 in that the input buffer circuit 20 further includesa voltage level detection circuit 400. Operations of the logic unit 100,the clock enable buffer 300 and the clock buffer 200 have already beendescribed with reference to FIG. 1.

The voltage level detection circuit 400 may selectively provide theclock enable signal CKE to the clock enable buffer 300 according to alevel of a power supply voltage VDD in the power-up mode when the powersupply voltage VDD is initially applied to the semiconductor memorydevice.

FIG. 5 is a circuit diagram illustrating an example of the voltage leveldetection circuit 400 in FIG. 4 according to some example embodiments.

Referring to FIG. 5, the voltage level detection circuit 400 includes acomparator (COMP) 410, a switching unit 420 and a resistor R. Thecomparator 140 compares a level of the power supply voltage VDD and atarget level Vt to provide a comparison signal CPS based on thecomparison result. For example, when the level of the power supplyvoltage VDD is lower than the target level Vt, the comparison signal CPSmay be a first logic level (i.e., logic low level). Also for example,when the level of the power supply voltage VDD is equal to or higherthan the target level Vt, the comparison signal CPS may be a secondlogic level (i.e., logic high level).

The switching unit 420 may include a switch 421 which is controlled inresponse to the comparison signal CPS. For example, when the level ofthe power supply voltage VDD is lower than the target level Vt, andthus, the comparison signal CPS is a logic low level, the switch 421 isconnected to a terminal 422. Therefore, the clock enable buffer 300 ispulled-down to the ground voltage GND. Also for example, when the levelof the power supply voltage VDD is equal to or higher than the targetlevel Vt, and thus the comparison signal CPS is logic high level, theswitch 421 is connected to a terminal 423. Therefore, the clock enablesignal CKE is provided to the clock enable buffer 300. The voltage leveldetection circuit 400 pulls-down the clock enable buffer 300 to theground voltage GND when the level of the power supply voltage VDD islower than the target level Vt and thus, abnormal input of the clockenable signal CKE to the clock enable buffer 300 due to noises may beprevented. When the level of the power supply voltage VDD is equal to orhigher than the target level Vt, the clock enable signal CKE iscontinuously provided to the clock enable buffer 330, and the inputbuffer circuit 20 operates in a same manner as the input buffer circuit10 of FIG. 1.

FIG. 6 is a waveform diagram illustrating an operation of the inputbuffer circuit 20 of FIG. 4.

Referring to FIG. 6, the clock enable buffer 300 is pulled-down to theground voltage GND before a time when the level of the power supplyvoltage VDD is lower than the target level Vt. The clock enable signalCKE is not pulled-down to the ground voltage VDD while the clock enablesignal CKE is not activated during a time interval T1˜T2, i.e., when thelevel of the power supply voltage VDD is higher than the target level Vtand the clock signal CK is not (normally) input. The clock enable signalCKE is activated after a time T2 when the level of the power supplyvoltage VDD is higher than the target level Vt and the clock signal CKis normally input.

Although FIG. 6 illustrates an operation of the input buffer circuit 20of FIG. 4, FIG. 6 may illustrate operation of the input buffer circuit10 of FIG. 1 with respect the operations executed after the time T1.

FIG. 7 is a block diagram illustrating an example of an input buffercircuit according to still other example embodiments.

Referring to FIG. 7, an input buffer circuit 30 includes inverters 31,33, 37, 39 and 41, a buffer 32, a NOR gate 34, a NAND gate 42, aflip-flop 35 and transistors 36 and 38. The inverter 31 inverts theclock signal CK. The buffer 32 buffers the clock enable signal CKE to beprovided to the flip-flop 35. The inverter 33 inverts output of theinverter 31. The NOR gate 34 performs a NOR operation on outputs of theinverts 31 and 33. The flip-flop 35 transfers the buffered clock enablesignal CKE to a first electrode of the transistor 36 in synchronizationwith the output of the NOR gate 34. The inverter 37 inverts the outputof the inverter 31, and output of the inverter 37 is applied to a gateof the transistor 38. The transistor 38 has a first electrode connectedto a second electrode of the transistor 36 and an input of the inverter39, and a second electrode connected to an output of the inverter 39. Aninput of the inverter 41 is connected to the input of the inverter 39,and the inverter 41 provides the internal clock enable signal ICKE.

The NAND gate 42 performs a NAND operation on the clock signal CK andthe internal clock enable signal ICKE to provide the internal clocksignal ICK. The input buffer circuit 30 converts the clock signal CK tothe internal clock signal ICKE under the control of the clock enablesignal CKE. In addition, the clock enable signal CKE which isasynchronously input, is converted to the internal clock enable signalICKE by being strobed by the clock signal CK. That is, the input buffercircuit 30 generates the internal clock signal ICK by controlling theclock signal CK by the internal clock enable signal ICKE.

FIG. 8 is a block diagram illustrating an example of a semiconductormemory device according to example embodiments.

Referring to FIG. 8, a semiconductor memory device 500 includes a memorycore unit 510 having a memory cell array 520, a buffer unit 530 and aninput buffer circuit 550.

Although not illustrated, the memory core unit 510 may include variousother elements for writing/reading data to/from the memory cell array520. For example, the memory core unit 510 may include a senseamplifier, a column decoder, and a row decoder.

FIG. 9 is a block diagram illustrating an example of the buffer unit inFIG. 8 according to example embodiments.

Referring to FIG. 9, the buffer unit 530 includes a plurality of buffers531˜535 and a plurality of latches 541˜545.

Hereinafter, there will be a detailed description of the semiconductormemory device 500 with reference to FIGS. 8 and 9.

Each of the buffers 531˜535 compares an address ADDR and control signalsRAS, CAS, CS, and WE with a reference signal REF and buffers the addresssignal ADDR and the control signals RAS, CAS, CS, and WE in response toan activation of the internal clock enable signal ICKE. Each of thelatches 541˜545 latches respective outputs of the buffers 531˜535 insynchronization with the internal clock signal ICK to provide aninternal address IADDR and internal control signals IRAS, ICAS, ICS andIWE.

The input buffer circuit 550 may employ the input buffer circuit 10 ofFIG. 1. Therefore, the input buffer circuit 550 may include the clockenable buffer 300 that buffers the clock enable signal CKE to provide aninternal clock enable signal ICKE that is activated when the clocksignal CK is normally input, in response to the clock signal CK and theclock enable signal CKE, and the clock buffer 200 that buffers the clocksignal CK to provide the internal clock signal ICK, in response to anactivation of the internal clock enable signal ICKE. The internal clockenable signal ICKE is provided to each of the buffers 531˜535, andenablement of each of the buffers 531˜535 is determined based on theinternal clock enable signal ICKE. In addition, the internal clocksignal ICK is provided to each of the latches 541˜545, and a latchtiming for each of the outputs of the buffers 531˜535 is determinedbased on the internal clock signal ICK.

The input buffer circuit 550 may further include the logic unit 100 thatprovides the decision signal DS indicating whether or not the clocksignal CK is normally input in response to the clock signal CK and theclock enable signal CKE. Therefore, the clock enable buffer 300 buffersthe clock enable signal CKE to provide the internal clock enable signalICKE, in response to an activation of the decision signal DS.

The input buffer circuit 550 may be included in a semiconductor memorydevice or may be included in a memory module which having a plurality ofsemiconductor memory devices.

FIG. 10 is a block diagram illustrating a memory system according tosome example embodiments.

Referring to FIG. 10, a memory system 600 includes a central processunit (CPU) 610, a memory controller 700 and a memory 800 having aplurality of memory modules 810, 820, . . . , 8 n 0. The memory system600 may be implemented with various configurations such as an electronicdevice, a computing system, a computer and a terminal device. The memorycontroller 700 writes and/or reads data to and/or from the memory 800under the control of the CPU 610.

Each of the memory modules 810˜8 n 0 may includes each of memory devices811˜81 m, 821˜82 m, . . . , 8 n 1˜8 nm and each of a plurality of buffercircuits 910-9 n 0. Each of the memory devices 8 n 1˜8 nm of the memorydevices 811˜81 m, 821˜82 m, . . . , 8 n 1˜8 nm are non-volatile memorydevices, each storing operating characteristics of each of the memorymodules 810˜8 n 0. Other memory devices 811˜81 m, 821˜82 m, . . . arevolatile memory devices.

The operating characteristics may include RAS to CAS, CAS latency,refresh period, access time required for accessing the memory 900, aprecharge time, a memory capacity and a number of memory rows andcolumns.

Each of the memory modules 810˜8 n 0 may includes each of buffercircuits 910˜9 n 0. Each of the buffer circuits 910˜9 n 0 may includethe buffer unit 530 and the input buffer circuit 550 in FIG. 8 in someembodiments. Each of the buffer circuit 910˜9 n 0 may include the inputbuffer circuit 550 in FIG. 8 and each of memory devices 811˜81 m, 821˜82m, . . . , 8 n 1˜8 nm may include the buffer unit 530 in FIG. 8 in otherembodiments. Each of memory devices 811-81 m, 821˜82 m, . . . , 8 n 1˜8nm may include the buffer unit 530 and the input buffer circuit 550 inFIG. 8 in other embodiments.

The memory controller 600 controls each of the memory modules 810˜8 n 0according to characteristic of the data being processed. The memorycontroller 600 includes a data generating unit (DGU) 710, a commandgenerating unit (CGU) 720, a synchronization clock generating unit(SCGU) 730, a refresh controller (RC) 740 and a clock enable signalgenerating unit (CKEGU) 750.

The SCGU 730 generates the clock signal CK. The CGU 720 generatescontrol commands RAS, CAS, WE and CS for controlling each of the memorymodules 810˜8 n 0, in synchronization with the clock signal CK,transfers the control commands RAS, CAS, WE and CS to the memory modules810˜8 n 0 and locates a corresponding location of the memory 900 forinputting/outputting data.

The DGU 710 writes and/or reads data to and/or from the location of thecorresponding memory module located by the CGU 720.

The refresh controller 740 controls the refresh operation such that thememory 900 is refreshed according to the refresh period of the memory900. Each of the memory modules 810˜8 n 0 performs the refresh operationwhen the clock enable signal CKE is a logic high level.

The CKEGU 750 generates the clock enable signal CKE to each of thememory modules 810˜8 n 0. The clock enable signal CKE is generated insynchronization with the clock signal CK. Each of the memory modules810˜8 n 0 may receive the clock enable signal CKE having differentlevels, from the CKEGU 750 according to a data capacity required by theCPU 610. That is, each of the clock enable signals CKE1˜CKEn may beapplied to each of the memory modules 810˜8 n 0, and each of the clockenable signals CKE1˜CKEn may have different levels depending on the datacapacity required by the CPU 610.

Each of the clock enable signals CKE1˜CKEn may be selectively activateddepending on the data capacity required by the CPU 610, and each of thememory modules 810˜8 n 0 may be selectively enabled in response to eachof the clock enable signals CKE1˜CKEn. Some of the modules 810˜8 n 0,which receive a high-level clock enable signal CKE, perform requiredoperations under the control of the controller 700, and some of themodules 810˜8 n 0, which receive a low-level clock enable signal CKE mayenter into power-down modes. Therefore, current consumption required fordriving the memory 800 may be reduced by individually controlling thememory modules 810˜8 n 0 according to the required data capacity to beprocessed by the CPU 610.

Each of the buffer circuits 910˜9 n 0 may include the input buffercircuit 550 in FIG. 8 and thus each of the buffer circuits 910˜9 n 0 maybuffer the clock enable signal CKE to provide the internal clock enablesignal ICKE that is activated when the clock signal CK is normallyinput, and buffers the clock signal CK to provide the internal clocksignal ICK, in response to an activation of the internal clock enablesignal ICKE. Therefore, malfunction due to noises may be preventedbecause the internal clock signal ICKE is not activated before the clocksignal CK is normally input even when the clock enable signal CKE isactivated.

Each of the buffer circuits 910˜9 n 0 may include the input buffercircuit 20 in FIG. 4, and thus, each of the buffer circuits 910˜9 n 0may admit of the clock enable signal CKE in the power-up mode, when thelevel of the power supply voltage VDD is equal to or higher than thetarget level Vt. Therefore, malfunction due to noises may be prevented.

In addition, the CKEDU 750 may employ the input buffer circuit 10 ofFIG. 1 or the input buffer circuit 20 of FIG. 4. In this case, the CKEDU750 may provide the internal clock enable signal ICKE to each of thememory modules 810˜8 n 0.

FIG. 11 is a flow chart illustrating a method of controlling asemiconductor memory device according to some example embodiments.

Hereinafter, there will be a description of a method of controlling asemiconductor memory device with reference to FIGS. 1 and 11.

A decision signal DS indicating whether or not a clock signal CK isnormally input is provided in response to the clock signal CK and aclock enable signal CKE (S910). The decision signal DS is activated onlywhen the clock signal CK is normally input. The clock enable signal CKEis buffered to be provided as an internal clock enable signal ICKE inresponse to an activation of the decision signal DS (S920). The clocksignal CK is buffered to be provided as an internal clock signal ICK inresponse to an activation of the internal clock enable signal ICKE(S930). The semiconductor memory device operates in synchronization withthe internal clock signal ICK. Therefore, abnormal operation of thesemiconductor memory device may be prevented by preventing activation ofthe clock enable signal CKE due to noise generated when the clock signalCK is not normally input.

As mentioned above, it is prevented that the clock enable signal isactivated prior to the clock signal due to noise by controlling anactivation time point of the clock enable signal through the clocksignal and buffering the clock signal based on the clock enable signal.Therefore, example embodiments may be applicable to varioussemiconductor memory devices and memory modules.

The foregoing is illustrative of example embodiments and is not to beconstrued as limiting thereof. Although a few example embodiments havebeen described, those skilled in the art will readily appreciate thatmany modifications are possible in the example embodiments withoutmaterially departing from the novel teachings and advantages of thepresent inventive concept. Accordingly, all such modifications areintended to be included within the scope of the present inventiveconcept as defined in the claims. Therefore, it is to be understood thatthe foregoing is illustrative of various example embodiments and is notto be construed as limited to the specific example embodimentsdisclosed, and that modifications to the disclosed example embodiments,as well as other example embodiments, are intended to be included withinthe scope of the appended claims.

What is claimed is:
 1. An input buffer circuit of a semiconductor memorydevice, comprising: a logic unit configured to receive a clock signaland a clock enable signal, and to output a decision signal indicative ofwhether the clock signal is normally input; a clock enable signal unitconfigured to receive the decision signal, and to activate an internalclock enable signal, in response to an activation of the decisionsignal; and a clock signal unit configured to output an internal clocksignal, in response to an activation of the internal clock enablesignal.
 2. The input buffer circuit of claim 1, wherein the logic unitcomprises: an AND gate that performs an AND operation on the clocksignal and the clock enable signal to output the decision signal.
 3. Theinput buffer circuit of claim 1, wherein the logic unit configured tooutput a first logic value when the clock signal is different logicvalue from the clock enable signal and output a second logic value whenthe logic value of the clock signal is high and the logic value of theclock enable signal is high.
 4. A semiconductor memory device,comprising: a memory core unit that includes a memory cell array; abuffer unit that includes a plurality of buffers configured to providean internal address and internal control signals to the memory core unitin synchronization with an internal clock signal; and an input buffercircuit including: a logic unit configured to receive a clock signal anda clock enable signal, and to output a decision signal indicative ofwhether the clock signal is normally input; a clock enable signal unitconfigured to receive the decision signal and to activate an internalclock enable signal, in response to the clock signal and the clockenable signal; and a clock signal unit configured to provide theinternal clock signal, in response to an activation of the internalclock enable signal.
 5. The semiconductor memory device of claim 4,wherein the logic unit outputs activated decision signal when the clocksignal and the clock enable signal are logic high levels.
 6. Thesemiconductor memory device of claim 4, wherein the logic unit outputsthe decision signal having a logic low level when the clock signal andthe clock enable signal have different logic levels with respect to eachother.
 7. The semiconductor memory device of claim 4, wherein the clockenable signal buffer is configured to output activated internal clockenable signal when the decision signal is activated.
 8. A memory systemcomprising: a plurality of memory modules; and a memory controllerconfigured to generate clock enable signals to each of the memorymodules to control an operation of each of the memory modules, each ofthe memory modules including: a logic unit configured to receive theclock signal and corresponding clock enable signal and to output acorresponding decision signal indicative of whether the clock signal isnormally input; a clock enable signal unit configured to receive thedecision signal and to activate an internal clock enable signal, inresponse to the clock signal and the corresponding clock enable signal;and a clock signal unit configured to output the internal clock signal,in response to an activation of the internal clock enable signal.
 9. Thememory system of claim 8, wherein the logic unit outputs thecorresponding decision signal which is activated when the clock signaland the corresponding clock enable signal are logic high levels.
 10. Thememory system of claim 8, wherein the logic unit outputs thecorresponding decision signal having a logic low level when the clocksignal and the corresponding clock enable signal have different logiclevels with respect to each other.
 11. The memory system of claim 8,wherein each the enable signal buffer is configured to output activatedinternal clock enable signal when the corresponding decision signal isactivated.